From the OP

only one value no range of values

It seems IsotopeData["U235", "HalfLife", "Interval"] is the only way to get the range of values.

Thank you for the suggestion. I know this solution:

Entity["Isotope", "U235"]["HalfLife"]

And the solution for my problem is:

WolframAlpha["U235 half-life", {{"Result", 1}, "ComputableData"}]

or

WolframAlpha["U235 half-life", {{"Result", 1}, "QuantityData"}]

or

WolframAlpha["U235 half-life", {{"Result", 1}, "NumberData"}].

But the item "ComputableData" does not appear in the documentation of WolframAlpha on the help page of Mathematica. I want to extract this out of WolframAlpha because in some cases, you get sometimes the error message "Missing" as the result of Entity but in Wolfram|Alpha, I have found Data and I have seen those in Wolfram|Alpha.

Hi Peter,

I don't know how to get the range using WolframAlpha. Using IsotopeData

IsotopeData["U235", "HalfLife", "Interval"]
(* Interval[{2.215*10^16, 2.228*10^16}] *)

For some reason, the values are not Quantity objects, you just have to know that the units are seconds.